Hi Al:
I'm Antonio de la Torre, Agile instigator in Taiga.
The Gantt, like a stone-made-planning with dependent and linked tasks, is hard to fit in an agile approach.
But a Gantt idea, like an ordered list of tasks distributed along the way to know when this will finish, we can get it in Taiga.
So, for your planning ahead, and if your are not using Scrum, like it seems, you can create as much sprints as you need, like iterations or milestones, and put inside them the user stories (like tasks) that you are planning to develop.
If you estimate each user story, you can see the sum of points you have planned per sprint.
So, you can plan ahead when your project will finish.
About reflect dependency between user stories, you can do it with the user story's field "Related tasks".
And about projects with subprojects, is in Taiga roadmap and we hope it will be out soon.
Thanks!
Antonio